Network node and methods therein for packet data convergence protocol (PDCP) reordering

ABSTRACT

A network node 606,608 and a method for Packet Data Convergence Protocol (PDCP) reordering. The network node is operating in a wireless communications network 600. The network node buffers in order one or more first data units received out of order by a PDCP layer, wherein the one or more first data units are received from a lower layer during a first time period, and wherein the lower layer is a layer below the PDCP layer. When the first time period has expired, the network node forwards the one or more buffered first data units in order to an upper layer and starts a second time period. Further, the network node forwards, to the upper layer and in any order, one or more second data units received from the lower layer during the second time period.

TECHNICAL FIELD

Embodiments herein relate to a network node, and to methods therein.Especially, embodiments herein relate to Packet Data ConvergenceProtocol (PDCP) reordering.

BACKGROUND

Communication devices such as terminals or wireless devices are alsoknown as e.g. User Equipments (UEs), mobile terminals, wirelessterminals and/or mobile stations.

Such terminals are enabled to communicate wirelessly in a wirelesscommunication system or a cellular communications network, sometimesalso referred to as a cellular radio system or cellular networks. Thecommunication may be performed e.g. between two wireless devices,between a wireless device and a regular telephone and/or between awireless device and a server via a Radio Access Network (RAN) andpossibly one or more core networks, comprised within the wirelesscommunications network.

The above terminals or wireless devices may further be referred to asmobile telephones, cellular telephones, laptops, or tablets withwireless capability, just to mention some further examples. Theterminals or wireless devices in the present context may be, forexample, portable, pocket-storable, hand-held, computer-comprised, orvehicle-mounted mobile devices, enabled to communicate voice and/ordata, via the RAN, with another entity, such as another terminal or aserver.

The cellular communications network covers a geographical area which isdivided into cell areas, wherein each cell area being served by anaccess node such as a base station, e.g. a Radio Base Station (RBS),which sometimes may be referred to as e.g. an “eNB”, an “eNodeB”, a“NodeB”, a B node”, or a Base Transceiver Station (BTS), depending onthe technology and terminology used. The base stations may be ofdifferent classes such as e.g. macro eNodeB, home eNodeB or pico basestation, based on transmission power and thereby also cell size. A cellis the geographical area where radio coverage is provided by the basestation at a base station site. One base station, situated at the basestation site, may serve one or several cells. Further, each base stationmay support one or several communication technologies. The base stationscommunicate over the air interface operating on radio frequencies withthe terminals or wireless devices within range of the base stations. Inthe context of this disclosure, the expression Downlink (DL) is used forthe transmission path from the base station to the mobile station. Theexpression Uplink (UL) is used for the transmission path in the oppositedirection i.e. from the mobile station to the base station.

A Universal Mobile Telecommunications System (UMTS) is a thirdgeneration (3G) telecommunication network, which evolved from the secondgeneration (2G) Global System for Mobile Communications (GSM). The UMTSTerrestrial Radio Access Network (UTRAN) is essentially a RAN usingWideband Code Division Multiple Access (WCDMA) and/or High Speed PacketAccess (HSPA) for user equipment. In a forum known as the ThirdGeneration Partnership Project (3GPP), telecommunications supplierspropose and agree upon standards for third generation networks, andinvestigate enhanced data rate and radio capacity. In some RANs, e.g. asin UMTS, several radio network nodes may be connected, e.g., bylandlines or microwave, to a controller node, such as a Radio NetworkController (RNC) or a Base Station Controller (BSC), which supervisesand coordinates various activities of the plural radio network nodesconnected thereto. This type of connection is sometimes referred to as abackhaul connection. The RNCs and BSCs are typically connected to one ormore core networks.

Specifications for the Evolved Packet System (EPS), also called a FourthGeneration (4G) network, have been completed within the 3GPP and thiswork continues in the coming 3GPP releases, for example to specify aFifth Generation (5G) network. The EPS comprises the Evolved UniversalTerrestrial Radio Access Network (E-UTRAN), also known as the Long TermEvolution (LTE) radio access network, and the Evolved Packet Core (EPC),also known as System Architecture Evolution (SAE) core network.E-UTRAN/LTE is a variant of a 3GPP radio access network wherein theradio network nodes are directly connected to the EPC core networkrather than to RNCs. In general, in E-UTRAN/LTE the functions of an RNCare distributed between the radio network nodes, e.g. eNodeBs in LTE,and the core network. As such, the RAN of an EPS has an essentially“flat” architecture comprising radio network nodes connected directly toone or more core networks, i.e. they are not connected to RNCs. Tocompensate for that, the E-UTRAN specification defines a directinterface between the radio network nodes, this interface being denotedthe X2 interface.

In the 3GPP LTE, base stations, which may be referred to as eNodeBs oreven eNBs, may be directly connected to one or more core networks.

The 3GPP LTE radio access standard has been written in order to supporthigh bitrates and low latency both for uplink and downlink traffic. Alldata transmission is in LTE controlled by the radio base station.

Multi-antenna techniques may significantly increase the data rates andreliability of a wireless communication system. The performance is inparticular improved if both the transmitter and the receiver areequipped with multiple antennas, which results in a Multiple-InputMultiple-Output (MIMO) communication channel. Such systems and/orrelated techniques are commonly referred to as MIMO systems.

In a 3GPP LTE communications network, a Radio Link Control (RLC)protocol, such as the RLC protocol according to section 5.1.3.2 “Receiveoperations” of the 3GPP TS 36.322 standard, always performs reorderingto guarantee in-sequence order delivery of data units to a Packet DataConvergence Protocol (PDCP) and further on from there. Thus, thereordering functionality is performed to reorder data units received outof order to guarantee that the received data units are delivered in acorrect order. The RLC is a layer 2 protocol used by LTE on the airinterface. Further, the RLC is located on top of the 3GPP MAC layer andbelow the PDCP layer. The PDCP layer is a data link layer or a dataforwarding layer. The PDCP protocol in LTE, e.g. the PDCP protocolaccording to section 5.1.2.1.4 “Procedures for DRBs mapped on RLC AM andfor LWA bearers when the reordering function is use” of the 3GPP TS36.323 standard, does also have a function to perform reordering of itsProtocol Data Units (PDUs), which is used at times when the RLC does notmanage to guarantee in-sequence delivery, e.g. during times when the RLCis re-established, e.g. for handover etc., and when data is sent usingtwo parallel RLC protocols and different physical layer adaptationfunctions. This is sometimes referred to as dual connectivity.

The 3GPP New Radio (NR) communications network, e.g. the 5Gcommunications network, aims at providing larger bandwidths at higherfrequencies with more challenging radio coverage, and is expected tohave an increased dependency on PDCP anchored dual connectivity and/ormulti-connectivity.

As a result, it is agreed to require from the PDCP to always provide thereordering function, i.e. not only at times when lower layers arere-established or configured for dual connectivity. The complexity ofthe RLC is decreased such that it does not need to perform reorderingbut may deliver without delay directly after Service Data Unit (SDU)assembly. An SDU is a unit of data that has been passed down from anupper layer to a lower layer. The SDU has not yet been encapsulated intoa Protocol Data Unit (PDU) by the lower layer. In other words, the SDUof the lower layer is the input to the protocol of the lower layer andthe PDU of the lower layer is the output from the protocol of the lowerlayer. Thus, the input to a protocol of a layer may be referred to asthe SDU and the output of the protocol of the layer may be referred toas the PDU. Further, the SDU at any given layer (n) is the PDU of thelayer above (n+1). In effect the SDU is the payload of a given PDU. Thelayer (n−1) adds headers or footers, or both, to the SDU when formingthe PDU. In this disclosure the terms the RLC SDU and the PDCP PDU areinterpreted as being equal and used interchangeably. It follows that thePDCP will meet new challenges to continuously execute reordering, atleast at occasions when in sequence delivery to one or more layers abovethe PDCP is needed. The layer above the PDCP layer may be a data linklayer, a network layer, a transport layer, a session layer, apresentation layer or an application layer just to give some examples.

The reordering function in the LTE PDCP is using a t-Reordering timer tolimit the time to wait for missing PDCP PDUs. If one or moreout-of-sequence PDCP PDUs are received by the PDCP layer, from lowerlayers, e.g. from the RLC layer, i.e. there is one or more missing PDCPPDUs, the reordering function in LTE PDCP will do the following:

-   -   1. The one or more out-of-sequence PDCP PDUs are buffered and        not immediately forwarded.    -   2. The t-Reordering timer is started. Note that if t-Reordering        timer is already running, it shall neither be started again nor        additionally be started for each of the one or more missing        PDUs, i.e. only one t-Reordering timer is running per PDCP        entity at any given time. The PDCP entity may be some piece of        software running a separate instance of a full PDCP protocol        between a network node, such as an eNB or a gNB, and a network        node, such as UE, for a specific, so called, radio bearer. There        are different bearers in LTE, signalling radio bearers aka SRB        and data radio bearers aka DRB. There is one entity for each        such bearer, thus also a timer for each such bearer.    -   3. If more PDCP PDUs, e.g. some of the one or more missing PDCP        PDUs, are received out-of-sequence before t-Reordering expire,        they are buffered and not immediately forwarded to an upper        layer.    -   4. If the one or more missing PDCP PDUs are all received before        the t-Reordering timer expire, they are immediately forwarded        in-sequence to the upper layer, followed by an in-sequence        delivery of buffered PDUs to the upper layer.    -   5. But if instead the t-Reordering timer expires before the one        or more missing PDUs are all received, there is no more waiting        but instead only the buffered PDCP PDUs will be forwarded to        upper layers. If by any chance any of the one or more missing        PDCP PDUs is received after the t-Reordering timer has expired,        it will arrive too late and will be discarded.    -   6. The lower end of the reception window will be advanced to        match the latest PDCP PDU that has been forwarded to upper        layers.

The PDCP reordering functionality provides a robust way to ensurein-order delivery for PDCP PDUs that are received within a certain timeperiod, but at the cost of setting a limit for how late PDUs, e.g.packets, may arrive.

EP 3 063 909 A1 relates to techniques for aggregating data from awireless wide area network (WWAN) and wireless local area network(WLAN). In some aspects, a packet convergence entity (e.g., PDCP layerentity) communicates with first and second radio access technology (RAT)links. The packet convergence entity may determine from which of thefirst and second RAT links a data packet is received and may monitor asequence number value of each of the received data packets. The packetconvergence entity may perform one or more actions based on adetermination that the data packets are received out of order. Forexample, the packet convergence entity may deliver the data packets toan upper layer entity as they are received (e.g., in order or out oforder), may reorder the data packets and ignore data packet losses,and/or may request retransmissions of missing data packets

SUMMARY

An object addressed by embodiments herein is how to improve performancein a wireless communications network.

An aim of some embodiments disclosed herein is to overcome or mitigateat least some of the drawbacks with the prior art.

According to an aspect of embodiments herein, the object is achieved bya method performed by a network node, such as a Radio Network Node or acommunications device, for PDCP reordering. The network node isoperating in a wireless communications network.

The network node buffers in order one or more first data units receivedout of order by a PDCP layer. The one or more first data units arereceived from a lower layer during a first time period. The lower layeris a layer below the PDCP layer. The upper layer is a layer above thePDCP layer.

When the first time period has expired, the network node forwards theone or more buffered first data units in order to an upper layer andstarts a second time period.

Further, the network node forwards, to the upper layer and in any order,one or more second data units received from the lower layer during thesecond time period. Thereby, the one or more second data units arrivingtoo late to the PDCP layer to be buffered in order are forwarded to theupper layer in time for a reordering functionality of the upper layer.

The network node buffering in order one or more first data units, meansthat the one or more first data units are buffered in sequence numberorder.

In some embodiments, the one or more second data units are immediatelyforwarded to the upper layer, e.g. they are forwarded directly afterreception. The first and second time periods may be consecutive timeperiods. Further, the first time period may be shorter that the secondtimer period. In other words, the network node may be waiting for theshorter first time period for missing packets to deliver these in orderwithout waiting too long, and then may be waiting till a longer secondtime period for any late still missing packets and still deliver theseto upper layers before advancing a lower edge of a receive window. Bythe expression “advancing the lower edge of the receive window” whenused herein is meant that a lower end of the receive window is movedforward, i.e. that the lower end of the receive window is moved to ahigher sequence number. The purpose of “advancing the lower edge of thereceiving window” is to ensure that received data units that are too oldare discarded by the receiver entity. The receive window is sometimes inthis disclosure referred to as a receiving window and it should beunderstood that the terms may be used interchangeably. The receivingwindow comprises the first and second time periods.

According to another aspect of embodiments herein, the object isachieved by a network node, such as a Radio Network Node or acommunications device, for PDCP reordering. The network node isconfigured to operate in a wireless communications network.

The network node is configured to buffer in order one or more first dataunits received out of order by a PDCP layer. The one or more first dataunits are received from a lower layer and during a first time period.The lower layer is a layer below the PDCP layer. The upper layer is alayer above the PDCP layer.

Further, the network node is configured to forward the one or morebuffered first data units in order to an upper layer and to start asecond time period, when the first time period has expired.

Furthermore, the network node is configured to forward, to the upperlayer and in any order, one or more second data units received from thelower layer during the second time period. Thereby, the one or moresecond data units arriving too late to the PDCP layer to be buffered inorder is forwarded to the upper layer in time for a reorderingfunctionality of the upper layer.

In some embodiments, the network node is configured to immediatelyforward, to the upper layer, the one or more second data units. In otherwords, the network node may be configured to forward, to the upperlayer, the one or more second data units directly after reception. Thefirst and second time periods may be consecutive time periods. Further,the first time period may be shorter that the second timer period. Inother words, the network node may be configured to wait for the shorterfirst time period for missing packets to deliver these in order withoutwaiting too long, and then may be configured to wait till a longersecond time period for any late still missing packets and still deliverthese to upper layers before advancing lower edge of receive window.

According to another aspect of embodiments herein, the object isachieved by a computer program, comprising instructions which, whenexecuted on at least one processor, causes the at least one processor tocarry out the method performed by the network node.

According to another aspect of embodiments herein, the object isachieved by a carrier comprising the computer program, wherein thecarrier is one of an electronic signal, an optical signal, a radiosignal or a computer readable storage medium.

An advantage with some embodiments disclosed herein is that therequirement of in-order delivery is decoupled from the advancement ofthe lower edge of the receiving window, which means that it is possibleto use two different time periods, e.g. first and second time periods,for the forwarding of received PDCP SDUs:

-   -   A first time period, e.g. a shorter time period, T1 in which        in-order delivery is ensured for SDUs forwarded to upper layers.    -   A second time period, e.g. a longer time period, T2 for which        SDUs may be forwarded to upper layers but where they may be        forwarded out-of-order, and duplicate detection may optionally        be supported during this second time period.

Lower layers PDUs received by the PDCP that are older than the secondtime period, will be discarded because they will arrive outside thereceiving window. It is important to discard these late PDUs because thereceiver must keep track of when the sequence number space is wrappingto zero, e.g. a Hyper Frame Number (HFN) is incremented, to avoid thesender and the receiver to be out-of-sync with regards to the HFNnumber. By the terms receiver and sender when used herein is meanteither the case when the UE is the sender and the gNB/eNB is thereceiver (uplink traffic), or the case when the UE is the receiver andthe gNB/eNB is the sender (downlink traffic).

BRIEF DESCRIPTION OF DRAWINGS

Examples of embodiments herein will be described in more detail withreference to attached drawings in which:

FIG. 1 schematically illustrates an example of PDCP reordering andin-order delivery according to prior art;

FIG. 2 schematically illustrates embodiments of PDCP reordering andin-order delivery;

FIG. 3 schematically illustrates how the length of the reordering windowdepends on the t-reordering timer;

FIG. 4 schematically illustrates window to keep track of received PDUswhile the t-WaitForLatePDUs timer is running;

FIG. 5 schematically illustrates that less memory is needed in the PDCPreceiver if the t-Reordering timer may be set to a small value;

FIG. 6 schematically illustrates embodiments of a wirelesscommunications network;

FIGS. 7A and 7B are flowcharts depicting embodiments of a methodperformed by a network node;

FIG. 8 is a schematic block diagram illustrating embodiments of anetwork node;

FIG. 9 schematically illustrates parameters that may be used inembodiments of a network node; and

FIG. 10 schematically illustrates parameters that may be used inembodiments of a network node.

DETAILED DESCRIPTION

As part of developing embodiments herein, some drawbacks with the stateof the art communications networks will first be identified anddiscussed.

As previously mentioned, the prior art PDCP reordering functionalityprovides a robust way to ensure in-order delivery for PDCP PDUs that arereceived within a certain time period, but at the cost of setting alimit for how late PDUs, e.g. packets, may arrive.

FIG. 1 schematically illustrates re-ordering and in-order delivery ofthe LTE PDCP. In action 101, no PDUs are awaiting in the receivingwindow, which receiving window in FIG. 1 encompasses Sequence Numbers(SN) N−2, N−1, N, N+1, . . . N+7. In action 102, a PDU N arrives and isbuffered, but PDU N−1 and PDU N−2 are missing. Further, in action 102,the t-reordering timer is started. In action 103, when the t-reorderingtimer expires, e.g. when a time period corresponding to the receivingwindow has lapsed, the lower end of the receiving window is movedforward (in this example the receiving window then encompasses SNs N+1,N+2, N+10), and the PDU N is forwarded to one or more upper layers asindicated by the thick arrow in FIG. 1. In action 104, the PDUs N−1 andN−2 arrive too late, i.e. outside the receiving window, and aretherefore discarded.

From a view-point of the PDCP it might not be obvious that the discardsat action 104 is a drawback, but higher layers, such as a TCP layer, hasalso a reordering functionality and what is modelled as too late at thePDCP layer may not at all be too late for the reordering functionalityat that higher layer, e.g. the TCP layer. Instead, abetter-late-than-never delivery of packets with SNs N−1 and N−2 ataction 104 will help to decrease triggering of higher layer'sretransmission, such as a Retransmission Timeout (RTO) of the TCP layer,and thereby save bandwidth.

The better-late-than-never delivery may be accomplished by using alarger value for the t-Reordering timer, but that would obviously implythat PDCP PDUs already received out-of-sequence must reside longer inPDCP buffer before they may be forwarded to higher layers.

The amount of memory needed at the PDCP receiver, e.g. at a networknode, such as at an eNB for an uplink transmission or at a UE for adownlink transmission, is greatly dependent on the length of thet-Reordering timer. With a long timer value there will be a need topotentially store many PDCP PDUs in case of one or more missing packets.For the communications network which may need to handle thousands ofsuch data flow in parallel this extra memory requirement will be quitesubstantial.

A large value for the t-Reordering timer will also increase the risk:

-   -   that the upper layers on the sending side, e.g. at the UE for        uplink transmission or at the eNB for downlink transmission,        triggers RTO and starts to retransmit packets that is already        waiting in buffer at the PDCP receiver e.g. at an eNB for an        uplink transmission or a UE for a downlink transmission.    -   of head of line blocking such that one late packet for one TCP        flow will delay packets for other TCP flows which have no        missing packets. This may be quite harmful for the performance        for e.g. interactive flows such as Quick User Datagram Protocol        (UDP) Internet Connection (QUIC) and real-time video.    -   It may take longer time for the TCP transmitter, e.g. at the UE        for an uplink transmission or at the eNB or gNB for a downlink        transmission, to react to a sudden decrease in the available        throughput over the air interface, e.g. the radio interface,        because the t-Reordering timer may delay the detection of any        discarded packets due to congestion. The TCP transmitter is an        upper layer entity that handles the transmission of TCP packets.

An object addressed by embodiments herein is how to improve performancein a wireless communications network.

Embodiments described herein are related to the PDCP in a 5G newgeneration radio communications network. Some embodiments propose one ormore ways to make implementation of a PDCP reordering function moreefficient for an expected traffic pattern.

In some embodiments disclosed herein the legacy PDCP reordering functionis improved so that PDCP PDU's arriving late and outside the receivingwindow because the t-Reordering timer has expired, are not discarded,provided they are received within a certain time limit. An extra timeris proposed to be added to determine how long to wait for when theselate PDCP PDU's are discarded. Thus according to some embodimentsdescribed herein, reference may be referred to a first timer and to asecond timer. The first timer may be the t-Reordering timer and thesecond timer may be a t-WaitForLatePDUs timer. Further, a reference tothe first timer may be interpreted as a reference to a first period oftime and a reference to the second timer may be interpreted as referenceto a second period of time, and the terms timer, period of time, timeperiod may sometimes herein be used interchangeably. However, it shouldbe understood that the second period of time may be defined by the firstperiod of time and an offset value. Therefore, some embodimentsdisclosed herein only comprise a single timer.

Sometimes in this disclosure the terms data unit, PDU and packet areused interchangeably. Further, sometimes in this disclosure the term“PDU” is used when describing a method for handling the reception ofPDUs, and the term “SDU” is used when describing the forwarding of adata packet to higher layers. Furthermore, sometimes herein referencemay be made to layers in plural, e.g. when describing transmission of aPDU from lower layers to upper layers, but it should be understood thatembodiments described herein are equally applicable to single layers,e.g. a PDU may be transmitted from a lower layer to an upper layer, orto a combination of single and plural layers. In for example, dualconnectivity where there is two legs connected to the same PDCP entityreference may be made to lower layers in plural. Furthermore, it shouldbe understood that a reference to an upper layer is the same as areference to a higher layer, and vice versa.

It should be understood that embodiments described herein are equallyapplicable to a Radio Network Node (RNN), such as a gNB or an eNB, andto a communications device, such as a UE. Thus, for transmissions in thedownlink, i.e. when the RNN is transmitting to the communicationsdevice, a reference to a PDCP receiver should be understood as areference to the communications device, while for transmissions in theuplink a reference to the PDCP receiver should be understood as areference the RNN.

The RNN and the communications device may also be referred to as a firstand a second network node, respectively.

FIG. 2 schematically illustrates embodiments relating to the forwardingof the PDU N to one or more upper layers and the awaiting for late PDUsduring a t-Wait-ForLatePDUs time period.

In FIG. 2 three actions, actions 203-205, are shown. These actions maybe preceded by two actions 201 and 202 corresponding to actions 101 and102 of FIG. 1. Thus, in action 201, no PDUs are awaiting in thereceiving window, and in action 202 a PDU N arrives out of order and isbuffered, but PDU N−1, and PDU N−2 are missing.

In action 203, the t-reordering timer expires, the lower end of thereceiving window is not moved forward as described in relation toFIG. 1. Instead the receiving window is retained at its currentposition. Further, the PDU N is forwarded to one or more upper layersand the t-WaitForLatePDUs timer is started.

In action 204, the PDU N−2 arrives and is forwarded, e.g. immediatelyforwarded, to one or more upper layers. Since the PDU N−2 is arrived outof the receiving window it is forwarded to the upper layer out of order,i.e. it will be forwarded out of sequence number order.

In action 205, the t-waitForLatePDUs timer expires, the lower end of thereceiving window is moved forward, and the PDU N−1 is considered aslost.

As FIG. 2 shows, the timer t-WaitForLatePDUs is started whent-Reordering timer expires, and it is the t-WaitForLatePDUs timer thatis responsible for moving the lower edge of the receiving window oncethe t-WaitForLatePDUs timer expires. During the time when thet-WaitForLatePDUs timer is running, any late PDUs that are received bythe PDCP receiver, will immediately be forwarded to higher layers. Thus,they will be forwarded in any order to the higher layers, i.e. they maybe forwarded out of sequence number order to the higher layers.

By differentiating between the time when reordering is enforced and thetime when late packets are anyway forwarded, it is possible in manycases to decrease the length of the t-Reordering timer which will havethe advantage that spurious retransmissions of the TCP transmitter dueto longer latencies is reduced, head of line blocking is minimized, andmemory usage is reduced. The TCP transmitter is an upper layer entitythat handles the transmission of TCP packets. FIG. 3 schematically showshow the length of the reordering window depends on the t-Reorderingtimer, cf. FIGS. 3A and 3B, and how the reordering window may bedecreased when using a separate t-WaitForLatePDUs timer, cf. FIG. 3C.FIG. 3A illustrates a large reordering window using 18 bits sequencenumbers which gives 131072 entries if half of the window space is usedfor buffering PDUs. Thus, the memory needed for the reordering windowmay be quite large because usually a reference to the stored PCDP PDUneeds to be stored in each window entry, so that packets quickly can beforwarded to higher layers in order, i.e. in sequence number order, andalso the packets themselves need to be stored. As illustrated in FIG.3B, the reordering window may be shorter when a t-reordering timer isused, but the length of the reordering window will depend on the lengthof the t-reordering timer, and thus the reordering window may be largewhen the t-reordering timer corresponds to a long time period. In FIG.3C it is illustrated how the reordering window, which as mentioned abovedepends on the t-reordering timer, may be even shorter if late receivedpackets received outside the reordering window are allowed to beforwarded to higher layers.

Normally the t-WaitForLatePDUs timer does not require any memory, sinceit is only guarding the lower end of the receiving window and is henceused for knowing where the reception window starts. However, it may alsobe useful to use a duplicate detection functionality in the PDCP forthese late packets that may arrive. A duplicate detection function maybe implemented by using a window, e.g. a receiving window, associatedwith the t-WaitForLatePDUs timer, but where this window only needs onebit per window entry to indicate if a certain PDCP PDU has been receivedor not. Thus, in order to provide duplicate detection in the PDCPreceiver while the receiver is waiting for any late PDUs after thet-Reordering timer has expired, a window associated with thet-WaitForLatePDUs may be used to detect and discard duplicates. FIG. 4schematically shows how this window may be used. The memory needed forthis window, e.g. the receiving window, associated with thet-WaitForLatePDUs timer is rather small because only one bit is neededper entry to indicate if a PDU has been received or not.

Even though a window is needed for the duplicate detection mechanism theactual memory required for this window is reduced as compared to thewindow used for t-Reordering functionality, as schematically illustratedin FIG. 5. For example, assume a 5 Gbps throughput and an MTU size of1500 bytes. If the t-Reordering timer needs to be set to 80 ms because at-WaitForLatePDUs timer is not used, up to 33360 packets are needed tobe stored in the window corresponding to a 50 Mbyte memory space. Thiscorresponds to the prior art scenario. If instead both a t-Reorderingtimer set to 20 ms and a t-WaitForLatePDUs timer set to 120 ms to waitfor late PDUs are used, only 8340 packets are needed to be stored in thewindow corresponding to a 12.5 Mbyte memory space. Further, the windowto keep track of received PDCP PDUs while the t-WaitForLatePDUs timer isrunning has a size of 50040 bits corresponding to a 6 Kbytes memoryspace. Thus, the memory space required for some embodiments disclosedherein are lesser than the memory space required by the prior artsolution.

Therefore, some embodiments disclosed herein provides a second timerthat controls whether data units arriving later to a given entity thanthe expiration of a first timer is to be discarded or delivered on tofurther entities. The first timer is started when an out-of-order dataunit is detected. By the expression “an out-of-order data unit” whenused in this disclosure is meant that the data unit is received out ofsequence number order. In other words, an out-of-sequence data unit is adata unit received with a higher sequence number than the most recentdata unit received and there is a gap in the sequence numbers betweenthese two data units. The fact that one or more out-of-order data unitsare received, implies that there are one or more missing data units,some of which may be received at a later point of time while the firsttimer is still running, some even later while only the second timer isrunning and further some after the second timer expires. When the firsttimer expires all data units that has been received in sequence, i.e. upto the first missing data unit, are delivered and forwarded to upperlayers. When the second timer expires, data units of two types aredelivered and forwarded to upper layers. The first type of data unitsare those that were received out-of-order while the first timer wasrunning. The second type of data units are those that were missing whenthe first timer expired but which were received before expiry of thesecond timer. These two types of data units are typically delivered inthe order they appear in sequence, although they may also be deliveredin any order, i.e. in any sequence number order. Thus, the order is notimportant when the second timer expires. Further, when the second timerexpires, the receiver does not wait any longer. If any of the one ormore data units that were missing when the first timer expired are stillmissing when the second timer expires, their place and fragmentedpresence in data structures are cleared and subsequently received dataunits or fragments of same are immediately discarded. It should beunderstood that the PDUs are identified by sequence numbers. Therefore,a reference to a missing data unit may be interpreted as a reference toa data unit identified by a sequence number which is expected but hasnot been received, and a data unit which is received out-of-sequence maybe interpreted as a reference to a data unit identified by a sequencenumber which comes after the sequence number of some missing data unit.A reference to a data unit arriving too late may be interpreted as adata unit arriving after the expiry of the second timer and identifiedby its sequence number as a data unit that was noted to be a missingdata unit while the first timer was running, and was still missing whenthe second timer expired.

The expiration timer values of the first and second timers may be setbased on estimates of the round trip times between a sender and areceiver of a first level transport protocol of the data generatorentity, and the one-way latency between a second level sender andreceiver transport protocol. For example, the expiration timer valuesmay be estimated based on the round trip times between two networknodes, e.g. between a Radio Network Node and a communications device.

According to some embodiments, the first level is an IP-layer transportprotocol functionality such as a TCP, a UDP or a QUIC protocol, and thesecond level is an access network transport functionality, such as the3GPP PDCP, or the RLC protocol. The first level corresponds to a higherlayer and the second level corresponds to a lower layer.

Some embodiments herein disclose window based methods to keep track ofreceived PDUs related to the first and second timers.

Some embodiments herein disclose duplicated detection function of theimplemented window based methods wherein windows only needs one bit perwindow entry to indicate if a certain data unit has been received ornot.

Note that although terminology from LTE is used in this disclosure toexemplify the embodiments herein, this should not be seen as limitingthe scope of the embodiments herein to only the aforementioned system.Other wireless systems, such as for example a NR network, 5G network, anLTE network, a Wideband Code Division Multiple Access (WCDMA) network, aGlobal System for Mobile Communications (GSM) network, any 3GPP cellularnetwork, a Worldwide Interoperability for Microwave Access (WiMAX)network, a Wireless Local Area Network (WLAN), a Low Rate WirelessPersonal Access Network (LR-WPAN) as defined in e.g. IEEE 802.15.4, aBluetooth network, a SIGFOX network, a Zigbee network, a Bluetooth LowEnergy (BLE) network such as a Bluetooth Smart network, or a CellularInternet of Things (CIoT) network such as an Enhanced Coverage GSM-IoT(EC-GSM-IoT) network, a Narrow Band IoT (NB-IoT) network or a networkcomprising one or more wireless devices configured for Machine TypeCommunication (MTC) sometimes herein referred to as an eMTC network, mayalso benefit from exploiting the ideas covered within this disclosure.

Further, the description frequently refers to wireless transmissions inthe uplink, but embodiments herein are equally applicable in thedownlink.

In the following section, embodiments herein will be illustrated in moredetail by a number of exemplary embodiments. It should be noted thatthese embodiments are not mutually exclusive. Components from oneembodiment may be assumed to be present in another embodiment and itwill be obvious to a person skilled in the art how those components maybe used in the other exemplary embodiments.

Some exemplifying embodiments will now be described in more detail.

In the following, embodiments herein are illustrated by exemplaryembodiments. It should be noted that these embodiments are not mutuallyexclusive. Components from one embodiment may be tacitly assumed to bepresent in another embodiment and it will be obvious to a person skilledin the art how those components may be used in the other exemplaryembodiments.

It should furthermore be noted that, to anyone skilled in the art, thereare several realizations of the embodiments below with principallyequivalent functionality.

In addition, it should be noted that message names, parameters,information elements and field names may change during the course of thespecification work which implies that embodiments described herein stillapply as long as the principal function and/or use is the same.

FIG. 6 depicts an example of the wireless communications network 600 inwhich embodiments herein may be implemented. The wireless communicationsnetwork 600 may be a cellular communications network such as a NRnetwork, a 5G network, an LTE network, a WCDMA network, a GSM network,any 3GPP cellular network, or a short range communications network, suchas a WLAN, an LR-WPAN, a Bluetooth network, WiMAX network, a SIGFOXnetwork, a Zigbee network, a BLE network such as a Bluetooth Smartnetwork, or a CIoT network such as an EC-GSM-IoT network, a NB-IoTnetwork or an eMTC network, or a combination of one or more of theaforementioned communications networks just to mention some examples.

A Core Network (CN) 602 may be comprised in the communications network600 The core network 602 may be an NR core network, a 5G core network,an LTE core network, a WCDMA core network, a GSM core network, any 3GPPcellular core network, or a short range communications core network,such as a WLAN core network, an LR-WPAN core network, a Bluetooth corenetwork, WiMAX core network, a SIGFOX core network, a Zigbee corenetwork, a BLE core network such as a Bluetooth Smart network, or a CIoTnetwork such as an EC-GSM-IoT core network, a NB-IoT core network or aneMTC core network, or a combination of one or more of the aforementionedcommunications core networks just to mention some examples.

A Core Network Node (CNN), 604 may be comprised in or arranged incommunication with the core network 602. The core network node 604 maybe a Mobility Management Entity (MME) or a Serving GPRS Support Node(SGSN). The core network node is sometimes referred to as just a networknode 604.

A Radio Network Node (RNN), 606 is arranged and configured to operate inthe communication network 600. The RNN 606 is configured for wirelesscommunication with communications devices, e.g. communications devicessuch as a communications device 608, when they are located within acoverage area 606 a, e.g. a geographical area served by the RNN 606. Itshould be understood that the RNN 606 may serve or manage a plurality ofcoverage areas 606 a, even though only one is illustrated in FIG. 6 forclarity reasons. The one more coverage areas 606 a are sometimes in thisdisclosure referred to as one or more cells 606 a.

The RNN 606 may be a transmission point such as a radio base station,for example a gNB, an E-UTRA node, a LTE eNB, an eNB, an Node B, or anHome Node B, an Home eNode B, a Base Station Transceiver (BTS) or anyother network node being capable to serve a communications device in acommunications network, such as the communications network 600. The RNN606 may further be configured to communicate with the core network node604. The RNN 606 is sometimes referred to as just a network node 606.

A communications device 608 is operating in the wireless communicationsnetwork 600. The communications device 608, also sometimes referred toas a wireless communications device, a wireless device, a user equipment(UE), or a Mobile Station (MS), may be located in the wirelesscommunications network 600. For example, the communications device 608may be an Internet of Things (IoT) device, a user equipment, a mobileterminal or a wireless terminal, a mobile phone, a computer such as e.g.a laptop, a Personal Digital Assistants (PDAs) or a tablet computer,with wireless capability, or any other radio network units capable tocommunicate over a radio link in a wireless communications network. Itshould be noted that the term user equipment used in this document alsocovers other wireless devices such as Machine to Machine (M2M) devices,even though they are not handled by any user. In some embodiments, thecommunications device 608 is a stationary wireless device. Thus, thecommunications device 608 is sometimes in this disclosure referred to asa stationary communications device 608. By the expression “stationarywireless device” when used herein is meant that the communicationsdevice 608 is not moving. For example, the stationary communicationsdevice 608 is not moving when in use, e.g. during operation.

The communications device 608 is sometimes referred to as just a networknode 608. Further, the RNN 606, the communications device 608, and thecore network node 604, may be referred to as first, second and thirdnetwork nodes 608, 606, 604.

More specifically the followings are network node 606, 608 relatedembodiments:

The network node embodiments relate to FIGS. 7A, 7B and 8.

A method performed by a network node 606, 608, such as the RNN 606 orthe communications device 608, for PDCP reordering will now bedescribed. As previously mentioned, the network node 606,608 isoperating in the wireless communications network 600. The methodcomprises one or more of the actions below and it should be understoodthat actions may be combined and that actions may be performed in anysuitable order.

Action 701A,701B

The network node 606,608 buffers one or more first data units receivedout of order from a lower layer and during a first time period.Especially, the network node 606,608 buffers in order one or more firstdata units received out of order by a PDCP layer. In other words, thenetwork node 606,608 buffers in sequence number order the one or morefirst data units received out of sequence number order by the PDCPlayer. As mentioned above, the one or more first data units are receivedfrom a lower layer during a first time period. Further, the lower layeris a layer below the PDCP layer.

This action relates to Action 202 previously described and may beperformed by a buffering module, e.g. a buffering module 803, comprisedin the network node 608, 606, such as the RNN 606 or the communicationsdevice 608. The buffering module 803 may be implemented by or arrangedin communication with a processor 807 of the network node 608, 606. Theprocessor 407 and the buffering module 803 will be described in moredetail below.

Action 702A,702B When the first time period has expired, the networknode 606,608 forwards the one or more buffered first data units in orderto an upper layer. In other words, the network node 606,608 forwards theone or more buffered first data units in sequence number order to theupper layer. Further, the network node 606,608 starts a second timeperiod. The upper layer is a layer, e.g. a TCP layer, above the PDCPlayer.

The expiry of the first and second time periods may be determined by arespective first and second timer, or may be determined by the firsttimer and a PDCP sequence number offset. The PDCP sequence number offsetis an offset from the Last_Submitted_PDCP_RX_SN parameter. TheLast_Submitted_PDCP_RX_SN parameter tracks the sequence numbercorresponding to the last one of the first data units that are insequence. The Last_Submitted_PDCP_RX_SN may also be defined to indicatethe sequence number SN of the last PDCP SDU delivered to the upperlayers.

For example the first and second time periods may be calculated based ona multiplicity of the round trip time.

In some embodiments, the first and second time periods are set based onan estimate of round trip times between network nodes 606,608, e.g.between the network node 606,608 and another network node 606,608, orbased on a PDCP data unit one-way delay and its variance.

In some embodiments, the network node 606,608 associates a window withthe second time period, and for each entry of the window the networknode 606,608 indicates whether or not a certain data unit has beenreceived. Further, the network node 606,608 10 may discard a receiveddata unit when the received data unit is indicated as already beingreceived. Thus, an already received data unit will not be forwarded.

This action relates to Action 203 previously described and may beperformed by a forwarding module, e.g. a forwarding module 804,comprised in the network node 608, 606, such as the RNN 606 or thecommunications device 608. The forwarding module 804 may be implementedby or arranged in communication with the processor 807 of the networknode. The forwarding module 804 will be described in more detail below.

Action 703A,703B

The network node 606,608 forwards, to the upper layer, one or moresecond data units received from the lower layer during a second timeperiod. The network node 606,608 may forward, to the upper layer and inany order, the one or more second data units received from the lowerlayer during the second time period. Thereby, the one or more seconddata units arriving too late to the PDCP layer to be buffered in orderis forwarded to the upper layer in time for a reordering functionalityof the upper layer.

In some embodiments, the one or more second data units are immediatelyforwarded to the upper layer, e.g. they are forwarded directly afterreception. In other words, the network node 606,608 may forward the oneor more second data units to the upper layer directly after reception ofthe one or more second data units. The first and second time periods maybe consecutive time periods.

This action relates to Action 204 previously described and may beperformed by the forwarding module, e.g. the forwarding module 804.

Action 704B

In some embodiments, the network node 606,608 moves a lower end of areceiving window forward to a sequence number N+1 upon expiration of thesecond time period. In such embodiments, the second time period wasstarted at a sequence number N, and the receiving window comprises thefirst time period and the second time period. This action relates toAction 205 previously described.

To perform the method for PDCP reordering, the network node 606,608 maybe configured according to an arrangement depicted in FIG. 8. Aspreviously described, the network node 206,208 is configured to operatein the wireless communications network 200.

The network node 608, 606, such as the RNN 606 or the communicationsdevice 608, may comprise an interface unit, e.g. an input/outputinterface 800, to facilitate communications between the network node andother network nodes or devices. The interface may, for example, includea transceiver configured to transmit and receive radio signals over anair interface in accordance with a suitable standard.

The network node 608, 606, such as the RNN 606 or the communicationsdevice 608, is configured to receive, by means of a receiving module 701configured to receive, a transmission, e.g. a data unit, a data packet,a signal or information, from one or more network nodes. The receivingmodule 801 may be implemented by or arranged in communication with theprocessor 807 of the network node.

The network node 608, 606, such as the RNN 606 or the communicationsdevice 608, is configured to transmit, by means of a transmitting module701 configured to transmit, a transmission, e.g. a data unit, a datapacket, a signal or information, from one or more network nodes. Thetransmitting module 801 may be implemented by or arranged incommunication with the processor 807 of the network node.

As mentioned above, the network node 606, 608, such as the RNN 606 orthe communications device 608, is configured to buffer, by means of e.g.a buffering module 803 configured to buffer, one or more first dataunits. The buffering module 803 may be implemented by or arranged incommunication with the processor 807.

The network node 606, 608 is configured to buffer in order one or morefirst data units received out of order by a PDCP layer. The one or morefirst data units are configured to be received from a lower layer duringa first time period, and the lower layer is a layer below the PDCPlayer.

As mentioned above, the network node 606, 608, such as the RNN 606 orthe communications device 608, is configured to forward, by means ofe.g. the forwarding module 804 configured to forward, data units to anupper layer. The forwarding module 804 may be implemented by or arrangedin communication with the processor 807 of the network node.

The network node 606, 608 is configured to forward the one or morebuffered first data units in order to an upper layer when the first timeperiod has expired. Further, the network node 606, 608 is configured tostart a second time period. The upper layer is a layer above the PDCPlayer.

Further, the network node 606, 608 is configured to forward, to theupper layer and in any order, one or more second data units configuredto be received from the lower layer during the second time period.Thereby the one or more second data units arriving too late to the PDCPlayer to be buffered in order is forwarded to the upper layer in timefor a reordering functionality of the upper layer.

In some embodiments, the network node 606, 608 is configured to forwardthe one or more second data units to the upper layer directly afterreception of the one or more second data units.

As previously mentioned, the first and second time periods may beconfigured to be consecutive time periods.

In some embodiments, the network node 606, 608 is configured to move alower end of a receiving window forward to a sequence number N+1 uponexpiration of the second time period. The second time period isconfigured to be started at a sequence number N, and the receivingwindow is configured to comprise the first time period and the secondtime period.

The network node 606, 608 may be configured to set the first and secondtime periods based on an estimate of the round trip times betweennetwork nodes 606, 608 or based on a PDCP data unit one-way delay andits variance.

In some embodiments, the network node 606, 608 determines expiry of thefirst and second time periods by a respective first and second timer, orby the first timer and a PDCP sequence number offset.

The network node 606, 608 may be configured to associate a window withthe second time period, and for each entry of the window indicatewhether or not a certain data unit has been received. Further, thenetwork node 606, 608 may be configured to discard a received data unitwhen the received data unit is indicated as already being received.

In some embodiments, the network node 608, 606, such as the RNN 606 orthe communications device 608, is configured to perform, by means of oneor more other modules 805 configured to perform one or more furtheractions described herein. The one or more other modules may beimplemented by or arranged in communication with the processor 807 ofthe network node.

The network node 608, 606, such as the RNN 606 or the communicationsdevice 608, may also comprise means for storing data. In someembodiments, the network node 608, 606 comprises a memory 806 configuredto store the data. The data may be processed or non-processed dataand/or information relating thereto. The memory 806 may comprise one ormore memory units. Further, the memory 806 may be a computer datastorage or a semiconductor memory such as a computer memory, a read-onlymemory, a volatile memory or a non-volatile memory. The memory isarranged to be used to store obtained information, data, configurations,and applications etc. to perform the methods herein when being executedin the network node.

Embodiments herein for PDCP reordering may be implemented through one ormore processors, such as the processor 807 in the arrangement depictedin FIG. 8, together with computer program code for performing thefunctions and/or method actions of embodiments herein. The program codementioned above may also be provided as a computer program product, forinstance in the form of a data carrier carrying computer program codefor performing the embodiments herein when being loaded into networknode. One such carrier may be in the form of an electronic signal, anoptical signal, a radio signal or a computer readable storage medium.The computer readable storage medium may be a CD ROM disc or a memorystick.

The computer program code may furthermore be provided as program codestored on a server and downloaded to the network node.

Those skilled in the art will also appreciate that the input/outputinterface 800, the receiving module 801, the transmitting module 802,the buffering module 803, the forwarding module 804, and the one or moreother modules 805 above may refer to a combination of analogue anddigital circuits, and/or one or more processors configured with softwareand/or firmware, e.g. stored in the memory 806, that when executed bythe one or more processors such as the processors in the network nodeperform as described above. One or more of these processors, as well asthe other digital hardware, may be included in a singleApplication-Specific Integrated Circuitry (ASIC), or several processorsand various digital hardware may be distributed among several separatecomponents, whether individually packaged or assembled into aSystem-on-a-Chip (SoC).

Some Exemplifying Embodiments

In this sections, some exemplifying embodiments will be described inmore detail.

Some First Exemplifying Embodiments Using a Timer

FIG. 9 schematically illustrates some parameters that may be used in thePDCP receiver, e.g. the network node 606, 608, such as the RNN 606 foran uplink transmission or the communications device 608 for a downlinktransmission, to handle re-ordering and in-order delivery of PDCP SDUsand further, specifically as proposed by some embodiments, to providedelivery of late PDCP SDUs to higher layers even if they are receivedand delivered out-of-order.

As schematically illustrated in FIG. 9, the receiving window comprises afirst time window and a second time window. During the first time windowthe network node 606, 608 waits for late packets and keep them in order,e.g. in sequence number order. The first time window is sometimesreferred to as the reordering window. During the second time window thenetwork node 606, 608 waits for late, e.g. very late, packets withoutkeeping them in order. The late packets are received outside the firsttime window.

In the illustrated example five parameters are shown. A first parameteris a Lower_PDCP_RX_SN parameter indicating the sequence number of thelower edge of the receiving window. A second parameter is aWait_PDCP_RX-SN parameter indicating the sequence number of the lastsubmitted PDCP PDU that was delivered to the upper layer when thet-WaitForLatePDUs timer expired. A third parameter is aLast_Submitted_PDCP_RX_SN parameter indicating the sequence number ofthe last PDCP SDU that was submitted in-order to the upper layer. Itshould be understood that the data unit indicated byLast_Submitted_PDCP_RX_SN has already been delivered to higher layers,and is therefore not subject to reordering. The sequence numbers abovethis value are part of the reordering window because(Last_Submitted_PDCP_RX_SN+1) has not been delivered yet to higherlayers. A fourth parameter is a Reordering_PDCP_RX_COUNT parameterindicating the COUNT value of the PDCP PDU following the COUNT value ofthe PDCP PDU that triggered t-Reordering. The Reordering_PDCP_RX_COUNTparameter indicates the sequence number that the lower edge of thereordering window should be moved to when the t-Reordering timerexpires. A fifth parameter Next_PDCP_RX_SN indicates the sequence numberof the PDCP PDU that is expected to be received by the PDCP entity.

As in LTE, when the t-Reordering timer expires, all buffered andassembled SDUs are delivered to the upper layers. The variableLast_Submitted_PDCP_RX_SN is updated to track the SN corresponding tothe last of those SDUs that are in sequence. This mechanism is proposedin some embodiments to be reused for PDCP.

As in LTE, the t-Reordering timer is proposed to be used for advancingthe lower edge of the reordering window, but in some embodimentsdisclosed herein it is proposed to use an additional timer, called at-WaitForLatePDUs timer, to advance the lower edge of the completereceiving window, where the reordering window is a subset of thereceiving window. In this way, there will be a first faster process,that uses a smaller reordering (in-order-delivery) window handled by thet-Reordering timer, which ensures in-sequence deliveries to the upperlayers and enough time for the lower layers to perform retransmission.Further, there will be a second slower process, handled by thet-WaitForLatePDUs timer, which advances the lower edge of the receivingwindow and allows immediate deliveries of received PDCP PDUs with nore-ordering for PDCP PDUs received outside the reordering window butinside the receiving window.

While the t-WaitForLatePDUs timer is running, the PDCP receiver, e.g.the network node 606, 608, such as the RNN 606 for an uplinktransmission or the communications device 608 for a downlinktransmission, will continue to forward any SDU, e.g. any PDCP SDU, thatwas noted to be missing after the first process of in-sequence delivery,as soon as they may get fully received and assembled, i.e. withoutconcern of its sequence number and the order in which it gets to beforwarded.

If there is no missing PDUs when the t-Reordering timer expires, thetimer t-WaitForLatePDUs does not need to be used. If that is the case,the Last_Submitted_PDCP_RX_SN is a good marker of a lower edge of boththe reordering window and the in-order-delivery window, i.e. theLower_PDCP_RX_SN may be set to the Last_Submitted_PDCP_RX_SN.

If instead there are missing SDUs, the t-WaitForLatePDUs timer may bestarted if not already started to supervise a late out-of-sequencedelivery during which Lower_PDCP_RX_SN, i.e. the lower end of thereordering window, does not change.

Some Second Exemplifying Embodiments for Improved Window Handling at thePDCP Layer

In some embodiments, the receiving window of the PDCP receiver, e.g. thenetwork node 606, 608, such as the RNN 606 for an uplink transmission orthe communications device 608 for a downlink transmission, is controlledby the t-WaitForLatePDUs timer, while the t-Reordering timer is insteadcontrolling an upper subset of this window, which is the reorderingwindow. The reordering window may be visualized as a pushed window, i.e.a window which is pushed from its lower end. The event or action thatperforms the pushing is the in-sequence submission to higher layers,which, similar to LTE, is controlled by the variableLast_Submitted_PDCP_RX_SN that keeps track of that lower edge of thereordering window. For some embodiments, the lower edge of thereordering window is controlled by the variable Lower_PDCP_RX_SN, and isused to wait for late PDCP SDUs. The receiving window thus comprises twoparts: a sub window in the form of the reordering window, which ensuresin-order-delivery, and a trailing part which is used to wait for anylate PDUs but does not ensure in-order-delivery.

In some sub embodiments, the Last_Submitted_PDCP_RX_SN variable isupdated using the t-Reordering timer just like in LTE, and controls thelower edge of the in-order-delivery window, which is an upper subset ofthe receiving window.

In some sub embodiments, the Lower PDCP_RX_SN variable is updated usingthe t-WaitForLatePDUs timer, and this variable controls the lower edgeof the receiving window.

In some sub embodiments, when the t-WaitForLatePDUs timer expires, thelower edge of the PDCP receiving window will be moved forward to thesequence number for which the t-WaitForLatePDUs timer was started.

In some sub embodiments, the Wait_PDCP_RX_SN variable stores thesequence number for which the Lower_PDCP_RX_SN will be set to when thet-WaitForLatePDUs timer expires.

In some sub embodiments, the receiving window uses the variableWait_PDCP_RX_SN to keep track of the last SDU that was delivered toupper layers when t-WaitForLatePDUs was (re)started.

As a consequence of some embodiments, if the t-Reordering timer is setto 0 it means that the reordering window will have zero length, and thusno enforcement of in-order-delivery will be done, but any late PDCP SDUsreceived within the receiving window and which has not already beenforwarded will be forwarded directly to upper layers, even if they areout-of-order.

As another consequence of some embodiments, if the t-WaitForLatePDUstimer is set to 0 it means that the in-order-delivery window, i.e. thereordering window, will be exactly the same as the receiving windowbecause the t-WaitForLatePDUs timer will immediately expire oncestarted. Thereby, the lower edge of the receiving window will be thesame as the reordering window, and hence any late PDCP PDUs receivedwithin the receiving window will also be received within thein-order-delivery window, and thus in-order delivery will be maintainedtowards upper layers.

In some embodiments, the t-WaitForLatePDUs timer is started at expiry ofthe t-Reordering timer but only at occurrence of missing SDUs. In someother embodiments, the t-WaitForLatePDUs timer is started at the sametime as the t-Reordering timer. In such a case, the t-WaitForLatePDUstimer is set to a larger value, approximately equal or preferablyslightly less than a Round-trip Time (RTT) used by the higher layer,such as the TCP RTT. The reason for not forwarding packets that has beenstuck longer than a RTT is that the TCP does not keep transmittedsegments in memory for ever.

In some embodiments, the rest of the receiving window which is not inthe reordering window is mapped to an array of indicators that keepstrack of PDUs that have been received. This was described above withreference to e.g. FIG. 4. The array is used to detect duplicates, i.e.PDUs which have already been received. Thus, if the PDCP receiver, e.g.the network node 606, 608, such as the RNN 606 for an uplinktransmission or the communications device 608 for a downlinktransmission, receives a PDCP PDU which has an SN for which a PDCP PDUhas already been received, the PDCP will discard the packet.

Some Third Exemplifying Embodiments for Estimating the Timer Values Usedat the PDCP Receiver

In all these embodiments, the values of the t-Reordering timer and thet-WaitForLatePDUs timer may be set based on an estimate of the higherlayer protocol round trip time, e.g. the TCP RTT, referred here to asT_higherlayerRtt and an estimate of the PDCP PDU one-way delay and itsvariance referred here to as T_delay and T_delayVariance respectively,such as;

   If T_delayVariance < T_higherlayerRtt then  t-Reordering =alfa*T_higherlayerRtt  t-WaitForLatePDUs = T_higherlayerRtt Else IfT_delayVariance >= T_higherlayerRtt then  t-Reordering = T_delayVariance t-WaitForLatePDUs = 0 Endwherein alfa is a scaling factor between 0 to1.

Exemplifying starting values for an adaptive parameter settingsmechanism for the two timers are;

-   -   t-Reordering=3*HARQ RTT (e.g. 3*HARQ transmissions round trip        time in a 3GPP system like LTE, ˜16 ms)    -   t-WaitForLatePDUs=2*RLC ARQ RTT (e.g. 2*RLC ARQ transmissions        round trip time in a 3GPP system like LTE, ˜72 ms)

The PDCP PDU one-way delay T_delay may be measured via a ping programmethod between the UE and the RNN, and the variance, T_delayVariance,may be calculated from those measurements. When PDPC and RLC areimplemented in the same network node, e.g. in the eNB in LTE, the PDCPPDU one-way delay T_delay may be implicitly measured by checking thetime when sending a RLC data unit and then checking the time ofreceiving the corresponding RLC acknowledgement and calculate the PDCPPDU one-way delay T_delay, and then its variance, T_delayVariance, fromthose measurements.

The T_higherlayerRtt may also be measured by pings between the RNN andthe UE, and the RNN and the higher-layer protocol sender, e.g. anInternet server, and adding them together. The T_higherlayerRtt may alsobe implicitly measured by examining the higher-layer protocol headersfor time stamp values and matching data units with its correspondingacknowledgements.

In some first to third exemplifying embodiments described above, a timeris used to determine when to move the lower edge of the receivingwindow. In some fourth exemplifying embodiments to be described below,an offset, e.g. a fixed offset, is used instead to define the lower edgeof the receiving window.

Some Fourth Exemplifying Embodiments using a Fixed Offset Instead toDefine the Lower Edge of the Reordering Window

FIG. 10 schematically illustrates the use of a Wait_Delta_Offsetparameter to defined the start of the receiving window from theLast_Submitted_PDCP_RX_SN parameter.

Some fourth exemplifying embodiments is similar to some embodimentswherein a timer is used to move the lower edge of the receiving window,but the difference is that the lower edge of the receiving window isinstead set to an offset from the Last_Submitted_PDCP_RX_SN parameter.

When the word “comprise” or “comprising” is used in this disclosure itshall be interpreted as non-limiting, i.e. meaning “consist at leastof”.

Modifications and other variants of the described embodiment(s) willcome to mind to one skilled in the art having the benefit of teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is to be understood that the embodiment(s) herein is/arenot be limited to the specific examples disclosed and that modificationsand other variants are intended to be included within the scope of thisdisclosure. Although specific terms may be employed herein, they areused in a generic and descriptive sense only and not for purposes oflimitation.

The invention claimed is:
 1. A method performed by a network node,operating in a wireless communications network, for Packet DataConvergence Protocol (PDCP) reordering, the method comprising: bufferingin order one or more first data units received out of order by a PDCPlayer, wherein the one or more first data units are received from alower layer during a first time period, and wherein the lower layer is alayer below the PDCP layer; when the first time period has expired,forwarding the one or more buffered first data units in order to anupper layer and starting a second time period, wherein the upper layeris a layer above the PDCP layer; and forwarding, to the upper layer andin any order, one or more second data units received from the lowerlayer during the second time period, whereby the one or more second dataunits arriving too late to the PDCP layer to be buffered in order isforwarded to the upper layer in time for a reordering functionality ofthe upper layer.
 2. The method of claim 1, wherein the one or moresecond data units received from the lower layer during the second timeperiod are forwarded to the upper layer directly after reception of theone or more second data units.
 3. The method of claim 1, wherein thefirst and second time periods are consecutive time periods.
 4. Themethod of claim 1, further comprising, upon expiration of the secondtime period, moving a lower end of a receiving window forward to asequence number N+1, wherein the second time period was started at asequence number N, and wherein the receiving window comprises the firsttime period and the second time period.
 5. The method of claim 1,wherein the first and second time periods are set based on one of: anestimate of round trip times between network nodes; and a PDCP data unitone-way delay and its variance.
 6. The method of claim 1, wherein:expiry of the first time period is determined by a first timer; andexpiry of the second time period is determined by one of a second timerand a PDCP sequence number offset.
 7. The method of claim 1, furthercomprising: associating a window with the second time period, and foreach entry of the window indicating whether or not a certain data unithas been received; and discarding a received data unit when the receiveddata unit is indicated as already being received.
 8. A non-transitory,computer-readable medium storing computer-executable instructions that,when executed by at least one processor comprising a network node,causes the network node to perform operations corresponding to themethod of claim
 1. 9. A network node configured for Packet DataConvergence Protocol (PDCP) reordering in a wireless communicationsnetwork, the network node comprising: at least one processor; and atleast one memory storing computer-executable instructions that, whenexecuted by the at least one processor, configure the network node to:buffer in order one or more first data units received out of order by aPDCP layer, wherein the one or more first data units are configured tobe received from a lower layer during a first time period, and whereinthe lower layer is a layer below the PDCP layer; forward the one or morebuffered first data units in order to an upper layer when the first timeperiod has expired and start a second time period, wherein the upperlayer is a layer above the PDCP layer; and forward, to the upper layerand in any order, one or more second data units configured to bereceived from the lower layer during the second time period, whereby theone or more second data units arriving too late to the PDCP layer to bebuffered in order is forwarded to the upper layer in time for areordering functionality of the upper layer.
 10. The network node ofclaim 9, wherein execution of the instructions further configures thenetwork node to forward the one or more second data units to the upperlayer directly after reception of the one or more second data units. 11.The network node of claim 9, wherein the first and second time periodsare consecutive time periods.
 12. The network node of claim 9, whereinexecution of the instructions further configures the network node tomove a lower end of a receiving window forward to a sequence number N+1upon expiration of the second time period, wherein the second timeperiod is configured to be started at a sequence number N, and whereinthe receiving window comprises the first time period and the second timeperiod.
 13. The network node of claim 9, wherein execution of theinstructions further configures the network node to set the first andsecond time periods based on one of: an estimate of the round trip timesbetween network nodes; and a PDCP data unit one-way delay and itsvariance.
 14. The network node of claim 9, wherein expiry of the firsttime period is determined by a first timer; and expiry of the secondtime period is determined by one of a second timer and a PDCP sequencenumber offset.
 15. The network node of claim 9, wherein execution of theinstructions further configures the network node to: associate a windowwith the second time period, and for each entry of the window indicatewhether or not a certain data unit has been received; and discard areceived data unit when the received data unit is indicated as alreadybeing received.